Blow-out preventer



Ap 5, 1938. F. w. HILD BLOW-OUT PREVENTER Filed Aug. 26. 1935 4 Sheets-Sheet 2 INKENTOR.- 4

ATTORNEY.

April 5,1938. F, w. ILD A2,113,529 s BLOW-OUT PREVENTER l Filed Aug. 26, 1935 4 Sheets-Sheet 4' NVENTOR.

A TTORNE Y.

Patented Apr. 5, 1938 UNITED STATES 2,113,529 v BLOW-OUT PREVENTER Frederic W. Hild,

Los Angeles, Calif.

Application August 26, 1935, Serial No. 37,959

22 Claims.

My invention relates to control and prevention of blowouts of oil and gas wells, this application being a continuation-in-part of my co-pending application Serial No. 733,854, filed July 5, 1934, for Expanding seal.

An object of the present invention is to provide a preventer which eiects closure of the axial outlet of the well against either the angular faced kelly or the round drill pipe of the drill string.

Another object is to provide a rotating packer on the kelly, locked into a ram type preventer by the rams.

Still another object is to provide a double ram type preventer which may be operated by fluid pressure or by rotative power and apply equalized ram pressure on the drill string.

A further object is to provide a ram type preventer with controlled fluid pressure for expanding the ram packing to effectively prevent the escape of well fluid.

Another object is to automatically regulate the packing pressure and sealing effect.

Additional objects, benets and advantages of the invention are shown by the following description and the vaccompanying drawings.

Figures 1 to 4 inclusive are reproduced from the aforesaid Serial No. 733,854, said figures being briefly described as follows:

Figure 1 shows in elevation and in part section, the double opposed ram type preventer with expanding seal for packing against the escape of well fluid;

Fig. 2 shows a horizontal section taken on the line 2-2 of Fig. 1;

Fig. 3 is a vertical section through a ram and taken on the line 3-3 of Fig. 2;

Fig. 4 is an isometric view of the expanding seal packing of the ram;

Fig. 5 shows in vertical sectional elevation the invention embodied in a well installation;

Fig. 6 is a fragmentary vertical sectional View taken on the line 6-6 of Fig. 5, and shows the Kelly packer locked in the ram preventer;

Fig. 7 is a horizontal section taken on the line 'l-'l of Fig. 5;

Fig. 8 is a horizontal section taken on the line 8 -8 of Fig. 5;

Fig. 9 is a horizontal section taken on the line 9-9 of Fig. 5, and shows. the preventer rams engaging and locking the Kelly packer into the preventer body;

Fig. 10 shows in horizontal section the ram,

preventer of Fig. 5 closed against the round drill pipe:

(Cl. 16B-15) Fig. 11 shows in part diagram the arrangement for operating the rams and for equalizing the pressure against the drill pipe or other object engaged by the rams; and

Fig. 12 shows in diagram the forces of a pair of rams in contact.

Referringto Figs. 1 to 4 inclusive, the blowout preventer has a vertical cylindrical body I6 with an opening therethrough and centering in the vertical axis. A. flange union is secured to the preventer body at the lower end of opening I1 and is threaded onto well casing |8. The drill pipe I9 extends through the preventer body, the flange union and the casing. Two cylinders and 2| having a common axis, extend in opposite directions radially from the body I6. An opening 22 is just below these two cylinders for the flow of fluid laterally from the preventer. The cylinders 20 and 2| are bored to larger diameter than opening the cylinder 20 contains piston ram 23, while cylinder 2| contains piston ram 24. -The two cylinders and their contained parts being duplicates, the description of one should suillce for both.

Cylinder 2| is closed at its outer end by cylinder head 25. The head has two recessed pockets, one of which is the innerv pocket 26, and the other the outer pocket'or stuffing box 21. The two pockets are separated by a partition. A ram screw 28 passes through both pockets and is threaded into the head 29 of the ram .24 for moving the ram axially in the cylinder. The ram screw has a collar 30 which with a washer is seated in the inner pocket 26 against the partition'. A bushing 3| is threaded into the open end of pocket 26 for retaining the collar 3|) in the pocket, so that the ram screw 28 may be rotated but may not move axially xcept for the usual slight clearance. The neck of the screw extendsfrom the collar outward and is round and smooth except for the square or hexagon head at the outer end. An expanding seal 32 and a packing or wear strip 33Mare inserted in the stuilingbox 2l and bear against the neck of the screw 28. A cover plate 34 secured to the cylinder head retains the seal and wear strip in the stufling box. The ram 23 in cylinder 20 is operated by a screw 35 which is similarly sealed and packed. Any suitable means such as pin and slot for engaging the ram and the cylinder may be utilized to prevent rotation of the rams.

The inner faces 36 and 31 ofthe rams 24 and 23 respectively meet in the vertical axis of the preventer body. Each ram face has a half bore centering in the same axis, the half bore 38 of ram 24 registering with 31 of ram 23 for closing against the drill pipe I9 when the two ram inner faces are together. A channel 40 for conveying iiuid extends from opening I1 in the body I6 to the cylinder space 4| between the ram head and the cylinder head.

The ram has a hollow space 42 between ram head and ram face. Seated in the ram head is a valve 43. A stationary valve rod 44 having an end secured to the icylinder head passes through the valve, the valve rod having a head 45 in the ram interior 42. The head is so placed that it' will intercept and open valve 43 with the last bit of movement of the ramas it reaches closing position in the preventer body.

'Ihe ram is slotted longitudinally along its sides by slots 46 and 41 and across its face diametrically by slot 48 and around the half bore 38 circumferentially by slot 49, th-four slots being continuous and horizontal. The ram at its head is slotted circumferentially by the slot 50 into which merge slots 46 and 41, all of the slots forming a continuous groove.

A hollow expanding seal 5| having the same conformation as the groove is inserted into the groove and is secured to the ram at three points.

One is by the bolt 52 at the `axial center of the ram in the slot 49, the other two are at diametrically opposite points in the circumferential slot 5D. At the last two points the seal has inlet tubes 53 and 54 which pass through tapered holes in the ram, the large end of the taper opening into the ram space. Each tube is firmly held fluid tight in the ram by anysuitable means as for example by a tapered thimble and a threaded bushing locked by a pin. The expanding seal 5I may be divided at a suitable place on the circular part andthe divided ends closed, in order to facilitate placing .the expanding seal on the ram.

For operating the blowout preventer I5 the channel 48 equalizes the well pressure on both ends of the ram, otherwise during a blowout the pressure then developed might seriously interfere with closing the rams.

When the rams 23 and 24 meet and close against the drill pipe I9, the valves 43'wiil open and the well fluid then may enterthe hollow space 42 in the ram. The fluid then enters the hollow seals, the fluid pressure expanding them in all directions, forcing them firmly against each other and against the drill pipe or the ram faces and against the cylinder walls of the preventer body, thereby effecting fluid shut off from the preventer. It should be remembered that drill' pipe is not machined, is seldom truly round and also varies in diameter within appreciable limits. But the resilient ram seals expanded by their contained iiuid under pressure will manifestly conform to and pack iluid tight against these irregularities of contour and dimensions.

Since the metal faces of the rams cannot meet in iluid tight contact because their surfaceswill not be suiiiciently true and exact, the well fluid in the preventer below the expanding seals will act on the lower half of the ram faces, that is, on less than half of the end area of each ram, to push the rams apart.V Opposed and overcoming this force is more than twice that force due to the well fluid pressure on the full area at the other ends of the rams to force them together.

Before the seals are expanded there are two sets of forces at the rams. They are shown diagrammatically by Fig. 12in which the arrows indicate the directions and relative magnitudes of the forces. One Aset of forces |08 is parallel to the ram axis being due to the axial force lili of the ram stems; the other set of forces H2 is at right angles to the ram axis being due to the friction of the unexpanded seals against the cylinder walls and must necessarily be quite small to permit ready axial movement of the ram. The axial force lill of the ram stem is resolved into the smaller forces distributed over the ramfaces and against the drill pipe. As these forces onthe drill pipe approach tangency to the pipe, they diminish to zero. But upon expanding the ram seals, not only are new forces added as in the tangent zones at the drill pipe but the forces are all equal in magnitude and normal to the surfaces contacted by the seal packing. Moreover, as will be described these forces may be increased or diminished by the expanding means. Hence iiuidtight packing at all of the packed surfaces and complete shut oil' against escape of the well fluid are assured.

Referring to Figures 5 to 11, the ram preventer 55 is secured to the casing I8 and contains the Kelly packer 56 which slidably engages the kelly 51, the last named extending through the Kelly packer, the preventerland into the casing.

'I'he preventer 55 is generally similartovthe preventer i5 previously described, having the body 58 with vertical opening 59 therethrough and the two horizontal ram cylinders 68 and 6l,

containing the similar shaped rams 62 and 63 re- I spectively.

The preventer cylinders 60 and 6I are closed at their outer ends by cylinder heads 64 and 65 respectively. Both cylinders and their contents are alike in arrangement and details so that description of one group will suffice for both.

To the ram 62 is secured the ram stem 66 which extends through the cylinder head. Splined onto the stem 66 is a nut 61 the splines terminating in stem collars 68 and 69. The nut is threaded on its outer circumference, the threads engaging a rotatable sleeve 10 which is supported in ball bearings 1| and 12 in thebearing housing 13. 'Ihis housing is secured to the outer face of the cylinder head 64 from which the bearing housing projects outwardly.

The cylinder head has a hub 14 extending in wardly into the cylinder for containing a packing the sprocket rotation. Y,

A similar sprocket 11 on the similar sleeve. nut andstem arrangement will correspondingly move the ram 63 in cylinder 6|. The two sprockets 16 and 1,1 are chain connected to sprockets 18 and 19 which are on the ends of differential shafts 80 and 8l respectively. A differential gear 82 is interposed between the other ends of the two differential shafts. The differential gear has a drive gear meshing with a pinion on'the end of drive shaft 83 and a hand wheel 84 is on the other end of the drive shaft. It is obvious that rotative power applied to the drive shaft will cause the rams 62 and 63 to move forward or .back and will apply equal pressure against any object in their respective paths. Each ram may be moved by fluid pressure independently of the rotative means. This is made possible by spacing the collars on each stem a distance apart about equal to the `full ram stroke. Thus by moving the nut 61 until it meets the inner stem collar 68 and then admitting fluid into the cylinder, the ram will be forced forward. For such fluid operation, pipes 85 and 86 lead from cylinders 60 and 6| respectively to a 3- way valve 81. This valve has a port venting to the atmosphere and also a port connected by a pipe 88 to a source of fluid pressure 89 such as a pump. A pipe 90 leads from pipe 88 to the well casing or the casing head below the preventer rams. A check valve 9| is inserted in pipe 90 and a second check valve 92 is inserted in pipe 88 near the pressure Supply.

Thus by way of the three-Way valve 81, fluid under pressure from source 89 may flow through the check valve 92 into the two cylinders 60 and 6| and move the rams forward. The fluid from pressure source 89-is stopped by check valve 9| against flowing into the well casing. But when entire surfaces.

the well pressure exceeds the pressurefrom source 89, then this greater pressure fluid from the well will flow into the cylinders and urge the rams forward, the check valve 92 preventing the well fluid from flowing into the pressure source l|19. Obviously, operation of the rams by fluid pressure also provides equalized force against the drill pipe or other object engaged by the rams.

'Ihe rams of the preventer are grooved the same as described for the rams of Fig. 1 in order to receive packing. Thus a hollow expanding seal 93 is inserted in the bottom of the groove and a packing 94 is inserted on top of expanding seal 93. The seal is secured to the ram at three points ,by hollow bolts, all of which communicate with the interior of the seal. One bolt is at the axial center of the ram and the other two are at opposite points of the circular part of the seal. The last two hollow bolts facilitate the forcing out of air when filling the seal with liquid; after which these two outlets are closed fluid tight by suitable plugs.

A hole 9B through the ram stem 66 registers with the center hollow bolt 95. A hose 91 connecis the outer end of the ram stern with a pressure pump 98. A three-way valve 99 is inserted in the hose, one port of the valve venting to the atmosphere. By means of pump 98, a suitable liquid may be forced through the hose and ram stem into the hollow interior of the seal 93, thereby expanding the seal and forcing the packing 94 outwardly against the cylinder walls, the drill pipe and the face of the opposite ram.

The three-way valve permits regulating the fluid pressure in the seal and thereby its expansion. For example, the seal 93 may be lightly expanded to permit only moderate frictional pressure of the packing against the cylinder walls, so that the ram may be readily moved in either direction. When moved forward and meeting the drill pipe and the opposite ram, then slight additional ram movement will compress the packings and the seals at the faces of the rams, thereby increasing the liquid pressure within the seals and causing them to expand and force the packings into effective sealing contact throughout their Thus the expanding sealing action may be accomplished automatically by the rotative power means at the drive shaft 83, or by the fluid pressure means from source 89 or by the well pressure.

' In the hub 14 of the cylinder head the stem packing |02 is on top of expanding seal 15 for preventing the escape of fluid from the cylinder past the ram stem 66. 'Ihe expanding seal 15 has suitable inlet |03 from which a duct |04 leads tothe outer face of the cylinder head. A pipe |05 connects to the hose 91 so that the expanding seal 15 is subject to the same inflation and regu- `lation as the ram seal 93. That is, the unit pressure at the packings 84 and |02 will always be alike.

'Ihe interior of upper neck |06 of preventer body 58 has the segmented breech lock slots |01 and the correspondingly segmented shoulder |08 for 'receiving and passing the mating breech lock lugs |09 of Kelly packer 56.

The Kelly packer has the shell |0 on which are formed the breech lugs |09. Within the shell is a rotatable sleeve the lower interior portion of which fits slidably on the angular faced kelly 51. The upper part of the sleeve is offset outwardly to form the inner shoulder ||3 for receiving a compression ring ||4 which also slidably ilts the kelly. Seated on this ring is the conformable packer ||5 which packs against the kelly and the upper linterior of rotatable sleeve On top of the packer is upper compression ring ||6 which likewise slidably lits the kelly.

A bronze sleeved journal ||1 is threaded onto the upper end of rotatable sleeve |||y against the upper compression ring ||6 and thereby compresses the packer I5 to the desired initial packing pressure. Projecting radially outward as part of the bronze journal is the thrust collar I8. The shell ||0 has at its upper end the outward radial collar ||9 to which is securely bolted the cap |20. An annular space between the cap and the sleeve collar receives the thrust collar 8 of the bronze journal V| |1, the vertical sleeve of which is journaled in the cap |20. Below the shell collar I9 is the stationary packer |2| for packing against the shell ||0 and the upper interior bore |22 of the preventer body 58. The stationary packer |2| is seated on split seat ring |23, the latter resting on a shoulder |24 of the shell ||0.

The lower end of shell ||0 has two inner grooves, one of which contains the split sleeve guide bearing |25 and the other groove containing the packing |26 and expanding seal |21. Into the guide bearing is journaled the rotatable sleeve against the lower portion of which is forced the packing |26 urged by seal |21.

The seal is secured to' the shell by a hollow bolt which leads from the hollow interior of the seal to an opening |28 having a check valve |29 and closure plug in the side of the shell.

During drilling, the well fluid pressures which are quite variable, may range from atmosphere to substantial and often to veryI high values. As shown and described in my fio-pending application Serial No. 756,002, filed December 4, 1934, for Power measuring devices: to effect seal, the radial pressure of the packing on the rotating sleeve may be less than the well pressures sought to be contained. A packing pressure that is adequate for low or moderate pressures would be quite insufficient for the high pressures. Conversely, the appropriate packing pressure for containing high fluid pressures would cause excessive friction and wear during the lower pressures. Therefore, the packing pressure should always be less than and in fixed ratio to the contained fluid pressure. This can be done by means 75 of the force or pressure converter and the expanding seal.

The expanding seal |21 has a radially projecting cylindrical diaphragm |30, the interior of which communicates directly with the interior of the seal. The diaphragm |30 fits into the bore I3I of boss |32 on the side of the shell Ill, the bcss forming the body of the pressure converter |33. Within the bore |3I is the larger diameter part of a two diameter piston |34, the face of this larger diameter part bearing against the diaphragm |30. The smaller diameter part of piston |30 extends into a hole containing the thimble diaphragm |35, of flexible material such as rubber, the closed end of which bears against the smaller piston. The thimble diaphragm |35 is flanged to form a gasket between the outer end of boss |32 and a threaded bushing |36 screwed' onto the boss against the flanged gasket of the thimble diaphragm.

The bushing being hollow permits the well fluid to enter the thimble diaphragm, whereupon the pressure therein will force the piston |34 against diaphragm |30, thereby increasing the pressure in the expanding seal |21l and correspondingly increasing the packing pressure against the rotating sleeve Since the unit pressures at the ends of the two diameter piston |34 are inversely as the square `of their diameters, the packing pressure will be less in fixed ratio than the well pressure.

The cap |20 at its 4upper end is bored to receive the expanding seal |31 and packing |38 which bear against the upper exterior of bronze journal II1. A hood |39'threaded onto the cap retains the packing and seal in the cap. The seal is provided with a suitable inlet and check valve with closure plug. The purpose of this packing is to exclude mud and other foreign material from the journal and thrust bearings of bronze journal I|1 and from the sleeve guide bearing I 25. The pressure at packing |38 therefore may benormally moderate; however, in emergency this pressure may be increased to help to contain the well uids.

The Kelly packer 56 is assembled'on the kelly 51, and as it may pass through the ordinary rotary machine, the packer is lifted into and out of the main preventer 55 when adding or withdrawing drill pipe. Upon lowering into the preventer body, the breech lugs |09 of the packer must pass through the clearance spaces of the segmented shoulder |08 and the breech lock slots |01 in the upper neck I 06 of preventer body 58, until the seat ring |23 of the Kelly packer rests on segmented shoulder |08. Then by anysuitable means the Kelly packer shell ||0 is rotated a quarter turn, bringing the lugs |08 of the packer into sliding contact with the sloping or thread-like upper shoulders of Wrench lock slots |01. The sloping faces of lugs and slots in contact are such that the quarter turn forces the shell ||0 downward so that the shell collar I|9 forces the stationary packer |2| downward onto the seat ring |23 to fluid tight contact with the shell I0 of the Kelly packer and the bore |22 of the preventer body 58. The preventer rams 62 and 63 are then moved against the flattened sides of the shell I0 so that the Kelly packer is firmly secured into the pre venter 55. It is plain that only the parts of the Kelly packer 56 which are in sliding contact with the kelly 51 may rotate with the kelly, none of the other parts may rotate.

When the well fluids rise and exert pressure on the Kelly packer, the seat ring |23 may be the general arrangement, the association of the several cooperating parts and the application of my invention without departing from the spirit thereof or the principles herein set forth.

I claim:

l. In a sealing device around the exterior of a pipe passing through a casing head, a closure member adapted to be moved transversely of the pipe axis, a hollow. expansible sealing member adapted to engage the exterior surface of the pipe, and carried by the closure member, means for moving said closure member to place the sealing member into engagement with the said surface, and means for passing uid under pressure into said sealing member for causing said sealing member to apply a sealing force against the pipe.

2. In a casing head adapted to receive a pipe, a member movable in the casing head and adaptn ed to engage the exterior surface of the pipe,

means for moving said member into position for engaging the said surface, a hollow expansible seal on said member, and means for passing fluid under pressure into said seal f or applying a sealing force on the pipe.

. 3. In a casing head of the valvular ram type, a hollow expansible member on an end face of l the ram and extending around at least a part of the periphery of the ram, and means for passing fluid under pressure into said member for causing said member to apply a sealing force at the ram against surfaces contacted by the ram, for preventing the escape of well fluid past the ram.

'4. In a casing head of the valvular ram type,

aram movable in the casing head, a hollow conformable sealing member on an end face of the ram and extending around at least a part of the periphery of the ram, means for filling said member with fluid, and means for moving the ram against an opposing surface at the end face of the ram thereby to increase the'fluid pressure in said conformable sealing member for applying a sealing force on the surfaces contacted by the ram.

5. In a sealing device around a pipe passing through a blow-out preventer of the piston ram type, a hollow expansible member arranged to be supported on the ram, said member having a portion extending around at least a -part of the ram periphery, as well as an arcuate portion corresponding to the curved surface of the pipe, said portions being united to form a single hollow space, and means for passing fluid under pressure into said member.

6. In a sealing device around a pipe passing through a blow-out preventer of the piston ram type. a hollow expansible member arranged to ,be supported on the ram, said member having a portion extending around at least a part of the ramperiphery, as well as an arcuatev portion corresponding to the curved surface of the pipe, said portions being united to form a single hollow space, packing between said member and the surface to be sealed, and means for passing fluid under -pressure into said member.

7. In a sealing device around a pipe passing 2,113,629 e" through a blow-out preventer of the piston ram type, a hollow expansible member arranged to be supported on the ram, said/member havinga portion extending around at least a part ofjthe ram periphery, as well as a portion adapted to engage the pipe, and a pair ofv diametrically opposite straight portions adjacent the periphery of the, ram and lconnecting said other 'nportions to form a single hollow space, and means for passing fluid under pressure into said member.

8. The combination as set forth in claim l1, in which said means whereby fluid pressure can be used to expand the seal,.includes a valve member opened in response to the arrival of the closure member near closing position...

9. 'I'he combination as set forth -in claim 1,\in

v which said means whereby fluid pressure can be used to expand the seal, includes means respond- Iing automatically to closing movement of the closure member to admit well fluid under pressure into the sealing member.' y d 10. A ram type blow-out preventer, comprising a hollow expanding sealing member carried by the ram and adapted to cooperate with an. element passing the ram, and means for pumping uid under pressure into the sealing member.

11. Ina ram type blow-out preventer, a hollow expanding sealing member carried bythe ram and adapted to cooperate with an element passing the lram, rotative means for moving the ram axially, and4 means for employing ud pressure to expand the member in response to movement of the ram. l

12. In a ram type blow-out preventer, a ram, a stem therefor for transmitting an axial force to the ram, an expansible hollow sealing member carried by the ram face, and means for supplying fluid pressure to the member and through th stem.

13. In a ram type blow-out preventer, a stem for the ram, an expansible hollow sealing member carried by the ram face, means for supplying fluid pressure to the member through the stem,

and means acting on the ram to urge it to closed position, said last named means operative to increase the fluid pressure in the .sealing member.

14. In a ram type blow-out preventer, a pair of rams adapted to cooperate with surfaces passing between the rams, a common means for moving both rams together or apart, and means ensuring that the forces exerted by each of the rams against the surfaces are equalized, comprising a differential gear transmission between the common means and the rams.

15. In a ram type blow-out preventer, a pair of rams adapted to cooperate with surfaces passing between the rams, means for optionally moving the rams either by rotative power or by uid pressure, and means cooperating with the rams when rotative power is utilized to equalize the forces exerted by each of the rams against the surfaces. f

16. In a blow-out preventer adapted to cooperate with the Kelly bar, a shell having a breech lock connection with the preventer'` hody, a pack- `er structure supported by the shell and adapted to pack against the Kelly bar passing through the shell, and means comprising a pair of rams in the preventer body forengaging and locking said shell in the preventer body.

17. In a ram type blow-out preventer, adapted 4 rotative movement.

to cooperate with a-Kelly bar, a shell having a breech lock` connection with the preventer body, a rotatable packer structure supported by thel shell, and rams having an axis transverse to that of the kelly, as wellas surfaces adapted to engage the shell when the rams are forced toward the axis of the'preventer, for locking said shell against 18. In a blow-out preventer, a', hollow body through which'a drill string' is adapted to pass,

a shellsupported in the body, a rotatable sleeve rotatably guided in the shell, a packer carriedon an internal shoulder of the sleeve, a journal member joined to the sleeve and compressing the surfaces adapted to be placed-in contact with each other; and means whereby a sealing pressure is obtained in the sealing members, the pressure being so directed against the drill stringas to provide substantially 'uniform `sealing lpressure over all of the contacted area.

' 20. In a sealing device around a pipe passing through a casing head, a movable closure member,

a ohollow expansible sealing member adapted to engage the pipe and carried by said closure member, means for moving said closure member linearly in adirection transverse to the pipe axis to place the sealing member into engagement with the pipe, and means for passing fluid under pressureinto said sealing member for causing the sealing member to apply a sealing force against the pipe.

21. Means for sealing around the periphery of a substantially cylindrical object, including a plurality of arcuate, expansible members adapted to cooperate -with each other to embrace substantially the entire periphery of the object, 'the abutting ends of said members being adapted to form a tight joint between adjacent pairs of members upon creation of pressure in the members, movable means for pressing the members against the object, and means fo r filling the members with fluid, whereby pressure lis created in the members, which is of uniform value, normal to the periphery at 'all points, and effective to urge the ends of adjacent pairs of said members together.

22. Means for sealing around the periphery of a substantially cylindrical object, including a pair of cooperating arcuate expansible members, each having a surface embracing a portion of said periphery approximately in extent, and having a wing at each end of said surface, whereby when f said. members are pressed against the object sub- -said members with uid, -whereby pressure is created in each of the members which is of uniform value, normal to the periphery at all points, and effective to urge cooperating pairs of wings together.

FREDERIC W. HILD. 

